Label-Free Chemical Imaging of Latent Fingerprints with Stimulated Raman Scattering Microscopy.

Fingerprints have long been the gold standard for personal identification in forensic investigations. Methods for cultivating and enhancing the visualization of latent fingerprints (LFPs) are continuously evolving. One important challenge is to identify suspicious chemicals present in fingerprint residues, which requires chemical imaging capability. Recently, vibrational spectroscopy has shown that LFP analysis through tape-lift, Raman mapping, and multivariate data analysis presents a useful tool for forensic investigation. However, there are still major difficulties in terms of acquisition speed, poor spatial resolution, and lack of sensitivity. This paper demonstrates the feasibility of stimulated Raman scattering microscopy to quickly and easily extract LFP patterns from different substrates. Contrary to what has been reported, no obvious fingerprint degradation or lipid diffusion is observed with either glass or stainless steel substrate. Importantly, we demonstrate that trace exogenous chemicals can be detected in fingerprints. We further demonstrate an improvement in directly acquiring a LFP pattern lifted from tape by spectrally removing signals from tape.